The Cardiovascular System

The heart MUST move the blood through…

vessels!

Frank-Starling Law

The heart MUST pump all blood that returns to it and its force of contraction is partially determined by how much blood returns to it (how much venous return stretches its sarcomeres)

• There is a length-tension relationship in cardiac muscle

• Force of contraction is ALSO regulated by the autonomic nervous system

Pulmonary Circuit

• From right side of heart to the lungs

• Blood picks up O2 and drops off CO2

• Returns to left side of heart

Systemic Circuit

• From left side of heart to all body cells

• Blood drops off O2 and picks up CO2 and other metabolic wastes

• Also distributes hormones, stored nutrients (glucose, triglycerides, etc) immune cells, and immunoglobins around the body

• Returns to the right side of the heart

Blood is composed of…

• formed elements (cells, platelets)

• Plasma

The _____ is the pump!

Heart

The vasculature (blood vessels) distributes blood to all body cells

Arteries, arterioles, venules, veins

What are the structural differences between these arteries, arterioles, venules, and veins?

• Arteries and arterioles have thick, muscular, elastic walls with small lumens to handle high-pressure blood flow away from the heart.

• veins and venules have thin, less muscular walls with large lumens and valves to manage low-pressure blood returning to the heart, preventing backflow

Pressure gradient

There must be a pressure gradient for fluid to flow from one place to another

• If there is no pressure gradient, then there will be no flow

The difference in pressure between two points on a vessel determines the ______ .

flow rate (volume per unit time)

• 40mmHg and 15mmHg will have a greater flow rate

Oneway valves prevent…

backflow if pressure builds up on one end

Blood pressure is highest at or near its source (the heart)

Decreases as it progresses

Note the dynamic drop in pressure by the time blood gets to the capillaries

• Allows for slower movement to facilitate transfer of gases, waste, and nutrients

• Capillaries are also very delicate

The heart is responsible for getting blood to tissues, not for bringing low pressure blood in the venules and veins back to it

There are two other mechanisms for this

How is venous return accomplished?

For body parts above the heart, it’s mainly gravity but for body parts below the heart…

• Sympathetic efferent pathways stimulate greater activity and efficiency in both pumps when activity levels increase